The objective of this project is to investigate the hormonal mechanisms that are responsible for linear growth. Principal areas of investigation include studying the effects of growth hormone and sex steroid administration on linear growth in patients with Turner's syndrome and delayed puberty. In addition, we are studying the mechanism of catch up growth in small for gestational age infants and in a primate model. We are also attempting to define the optimal dose of hydrocortisone for growth in patients with adrenal insufficiency and of thyroid hormone in patients with hypothyroidism. We are also studying the effects of administering somatomedin-C, a growth hormone- dependent peptide, to hypophysectomized cynomologus monkeys to determine its growth-promoting activity. In addition, we are examining the effect of inducing pubertal delay in children with extreme short stature, in order to prolong prepubertal growth prior to the pubertal spurt and possibly enhance ultimate height by delaying epiphyseal fusion. We are also investigating the effects of growth hormone therapy on the adult height of non- growth-hormone deficient children with short stature through a randomized, double-bind, placebo-controlled clinical trial. In addition, we are investigating the growth hormone secretory dynamics in patients with hypophosphatemic rickets. Finally, we are studying the effects of growth hormone-releasing factor on linear growth in growth hormone-deficient children by using different treatment regimens in order to optimize growth.